Micro-fluid ejection devices, such as ink jet printers, continue to evolve as the technology for ink jet printing continues to improve to provide higher speed, higher quality printers. However, the improvement in speed and quality does not come without a price. The micro-fluid ejection heads are more costly to manufacture because of tighter alignment tolerances.
For example, some conventional micro-fluid ejection heads were made with nozzle plates (a form of a nozzle member) containing flow features. The nozzle plates were then aligned, and adhesively attached to a semiconductor substrate. However, minor imperfections in the substrate or nozzle plate components of the ejection head or improper alignment of the parts has a significant impact on the performance of the ejection heads.
One advance in providing improved micro-fluid ejection heads is the use of a photoresist layer applied to a device surface of the semiconductor substrate as a thick film layer. The thick film layer is imaged to provide flow features for the micro-fluid ejection heads. Use of the imaged thick film layer enables more accurate alignment between the flow features and ejection actuators on the device surface of the substrate.
While the use of an imaged photoresist layer improves alignment of the flow features to the ejection actuators, there still exist alignment problems and difficulties associated with a nozzle plate attached to the thick film layer. Misalignment between the ejection actuators and corresponding nozzles (e.g., holes) in a nozzle plate has a disadvantageous effect on the accuracy of fluid droplets ejected from the nozzles when the nozzles are formed in the nozzle plate before attaching the nozzle plate to the thick film layer. Ejector actuator and nozzle alignment also has an effect on the mass and velocity of the fluid droplets ejected through the nozzles.
Conventional nozzle plates have been made from metal or a polyimide material that was laser ablated then adhesively attached to the thick film layer. Use of such nozzle plates require an alignment step to assure that the nozzles correspond with the fluid ejector actuators and flow features in the thick film layer. In order to eliminate such alignment steps, photoimageable nozzle plate materials may be directly applied to the thick film layer on the substrate by spin coating or lamination techniques. Spin coating techniques may be used to apply the nozzle plate photoresist material to the thick film layer before the flow features are developed in the thick film layer. However, developing the flow features in the thick film layer after applying the nozzle plate materials to the thick film layer requires difficult processing techniques.
In the alternative, lamination techniques may be used to apply the nozzle plate materials to an imaged and developed thick film layer. However, typical dry films that are available are generally used for various printed circuit board applications which require fairly thick photoresist layers ranging from about 35 microns to about 50 microns in thickness. These typical thickness ranges may be too great to be used in a photoimageable nozzle plate process.
Traditional photoresist formulations are often unable to be screened down into a thin film and dried without becoming extremely brittle. Brittleness makes such formulations difficult to process onto a wafer. It is believed that the brittleness may be due to the room temperature properties of the resin components of the resist, since commonly used epoxy resins may be brittle crystalline solids at room temperature. Hence, a need exists for a specific photoresist formulation containing epoxy resins that may be capable of forming a thin film ranging from 1 to 30 microns in thickness.
Accordingly, there is a need for improved photoresist or photoimageable materials that may be used as nozzle materials that may be laminated as a thin film layer adjacent to a thick film layer of a micro-fluid ejection head structure.
Among other embodiments of the provided in the disclosure, there is provided an improved photoimageable nozzle member for a micro-fluid ejection head, a micro-fluid ejection head containing the improved nozzle member, and a method for making a micro-fluid ejection head.
In one embodiment, a photoimageable nozzle member for a micro-fluid ejection head is disclosed. The nozzle member may include a photoresist material derived from a composition comprising a high molecular weight phenoxy resin, a di-functional epoxy resin, a multi-functional epoxy resin, an optional adhesion enhancer, a photoacid generator devoid of aryl sulfonium salts, and an aliphatic ketone solvent. The nozzle member may have a thickness ranging from about 1 to about 50 microns.
In another embodiment, there is provided a method for making an improved micro-fluid ejection head. The method includes applying a photoresist thick film layer adjacent to a device surface of a substrate. A plurality of flow features are imaged in the thick film layer. The imaged first photoresist layer is developed to provide the plurality of flow features therein and to provide a substantially planar thick film layer surface. A thin film photoresist layer is applied adjacent to the thick film layer. The thin film photoresist layer has a thickness ranging from about 1 to about 50 microns and is derived from a thin film photoresist epoxy resin composition including a high-molecular weight phenoxy resin, a di-functional epoxy resin, and a multi-functional epoxy resin. A plurality of nozzles is imaged in the thin film photoresist layer. The imaged thin film photoresist layer is developed to provide a photoresist nozzle member adjacent to the thick film layer.
An advantage of at least some of the exemplary embodiments described herein is that lamination of a dry film photoresist layer adjacent to a substrate and thick film layer for a micro-fluid ejection head enables wafer level processing of the ejection head. Wafer level processing means that separate processing steps for the nozzle member and the semiconductor substrate may be eliminated in favor of photoimaging and developing the composite substrate containing materials providing the flow features and nozzles. Accordingly, laser ablation steps for the nozzle member as well as alignment tolerances, and adhesives, used to attach the nozzle member to the substrate may be avoided. Other potential benefits of the disclosed embodiments include reduction in raw materials required, potential improvement in ejection head performance, improvement in adhesion and durability of the composite substrate and nozzle member structure, and significant manufacturing cost savings.
For purposes of the disclosure, “difunctional epoxy” means epoxy compounds and materials having only two epoxy functional groups in the molecule. “Multifunctional epoxy” means epoxy compounds and materials having more than two epoxy functional groups in the molecule.